Pickling inhibitors



Patented Feb. 12, 1946 PICKLING INHIBITORS William H Hill, Mount Lebanon, Pa., assignor to American Cyanamid Company, New York, N. Y., a corporation of Maine No Drawing. Original application December 11,

v1940, Serial No. 369,562.

Divided and this application October 11, 1943, Serial No. 505,841

4 Claims.

This invention relates to the preparation of pickling inhibitors. More particularly, the invention relates to the preparation and use of aldehyde condensation products of the sulfides of polyamines as pickling inhibitors. This is a division of my co-pending application, Ser. No. 369,562 filed December 11, 1940.

Such substances inhibit the solvent action of pickling acids on metals but still permit the acid to clean and remove scale, rust, oxides and the like from the metal surface. In the past, a number of compounds have been used as inhibitors in acid cleaning and pickling baths, however, such preparations have not been very satisfactory when used as inhibitors. For example, some of these products though found to have satisfactory inhibiting effect are very difiicultly soluble in acids. In order to use them they have to be boiled in the concentrated acid before dilution with water to normal pickling strength; others are readily volatilized and hence lose their effectiveness, especially when used in a heated pickling bath; still others must be used in large proportions and are therefore neither economical nor efiicient.

It is the principal object of this invention to prepare a pickling inhibitor which is effective in extremely dilute proportions. A further object is to provide an inhibitor which is cheap and easy to make. A still further object is to prepare an acid soluble inhibitor. Other and further objects and advantages will become apparent in the description of the invention, particularly as given in the illustrative examples.

It has been found that the reaction products of polyamine sulfides with aldehydes are eflicient inhibitors for acid pickling and cleaning solutions. These products are readily soluble in various pickling baths in the required amounts necessary for effective operation. Only a very small amount, usually a fraction of one percent, of any inhibitor composition of this invention is sufiicient.

The products of this invention are prepared by making an aqueous or an alcoholic solution or slurry of the particular polyamine, passing hydrogen sulfide into the mixture until reaction ceases, filtering the solution where necessary and condensing the filtrate with an aldehyde, such as formaldehyde in aqueous solution. The condensation product is then dissolved in a diluted acid solution where it permits the acid of the pickling bath to attack the unclean or oxidized portions of the metal surface while protecting the clean portions from corrosive or further acid attack.

Thus, iron and steel articles coated with scale and dirt can be effectively cleaned while prevent- 5 ing substantial loss of the metal by its reaction with the pickling acid to liberate hydrogen. The advantage of an effective inhibitor is twofold: it allows the acid to dissolve the iron oxide, scale, etc., but it substantially prevents the pickling acid from attacking the metal surface itself.

Dissolution of metal in a pickling bath is undesirable because this weakens the acid bath and in addition causes a pitting and roughening of the surface. This is undesirable if a smooth 5 surface for subsequent painting or metal coating is desired.

In order that this invention may be more fully and clearly understood, the following examples are given:

Example I 50 cc. of. diethylenetriamine were diluted with 50 cc. of water and the solution saturated with hydrogen sulfide. A 40% aqueous solution of formaldehyde was added slowly and as long as a white, fibrous, precipitate formed. The precipitate, upon standing, became spongy and rubber-like and after being separated out, washed with water, dried at 105 C. yielded a light yellow, sticky, very viscous resin which darkened when heated to 145 C.

A pickling solution was prepared using 250 cc. of concentrated hydrochloric acid diluted with 500 cc. of water. Two tenths of one gram of the above diethylene-triamine sulfine resin was added and dissolved very easily in the diluted acid. Two blued (oxidized) nails were added and after approximately to 1 hour were bright. Even after 3 days in the solution the nails were bright and smooth and did not seem to show any material attack by the acid. After 7 days one nail still seemed unattacked while the other showed a very narrow slit at the tip, but both nails still remained bright and smooth.

EEG-7714718 II When dissolved in a pickling solution similar to that given in the above example (one tenth of one percent) this triethylene-tetramine sulfine resin also acted as an inhibitor and compared very favorably with the previous sulfine resin inhibitor. Only after 17 days submersion, could the more effective inhibition of the diethylenetriamine sulfine resin be noted. Then the nails from Exampic I looked better, one being almost unattacked, the other nail having a slit in its tip, while the nails from Example 11 showed more corrosion.

Example III 50 cc. of a 22% aqueous solution of monomethylamine was saturated with hydrogen sulfide. This mixture was reacted with an excess of formalin to yield a gray-white precipitate which was filtered, washed with water, and dried. The product was a monomethylamine sulfine resin.

Example IV Example V 50 cc. of diethanolamine were mixed with 50 cc. of water and the mixture saturated with hydrogen sulfide. Adding formalin gave, at first, a slight color change but heating the reaction mixture on a steam bath resulted in the formation of a white solid precipitate, which was filtered off, washed and dried. The product was a diethanolamine sulfine resin.

Example VI 50 cc. of triethanolamine were diluted with 50 cc. of water and the mixture saturated with hydrogen sulfide. This solution was reacted with an excess of formalin on a steam bath whereupon the solution became cloudy and a gray-white somewhat gelatinous precipitate formed which was filtered, washed with water and dried. The pr: duct was a triethanolamine sulfine resin.

A series of pickling solutions were prepared each containing 250 cc. of concentrated hydrochloric acid diluted with 500 cc. of water. Then one half of one gram of the inhibitors prepared according to Examples III to VI were added and two blue nails submerged in each. The result of these tests is given in the following table:

5 None Nails dissolved..-

The inhibitors in tests 1 to 4 did not dissolve very readily, but a sufiicient amount of each went into solution. 7

The compounds produced as above described are very effective acid inhibitors and require the addition of only very small amounts of a pickling bath in order to inhibit the solvent action of the acid in the bath on metal. In order to show the superiority of the products of this invention over the standard inhibitors of the trade, a commonly incorporated commercial inhibitor was used in one set of tests and the above polyamine sulfine resin in another set of tests. The efliciency of the products was determined in the following manner:

The inhibiting efficiency was determined by weighing small strips of scale-free steel, S. A. E.

* 1010, 26 gauge and size 3" x 4", comparing the loss in weight sustained in inhibited 5% sulfuric acid at 180 .C. 2 with the loss in weight sustained by similar pieces of steel in 5% sulfuric acid containing no inhibitor. Various strengths of inhibitor were used.

The inhibiting eficiency was then calculated from the following expression:

From these tests it will be seen that the acid inhibitors of this invention surpass, in efiiciency, the usual run of inhibitor now used commercially.

In a similar manner, various other sulfine resins and inhibited acid pickling solutions can be prepared. Thus, ethylene diamine, monobutyl amine, and cyclohexylamine sulfine resins among various others may be prepared, although the more active resinous inhibitors have been more specifically described above in the examples. Also various modifications of the processare possible, as for example a formaldehyde solution may be reacted with hydrogen sulfide and an amine then reacted with the product.

Although, in the examples given, formaldehyde has been specifically mentioned, any other aldehyde may be used such as paraformaldehyde, crotonaldehyde, acetaldehyde, among numerous others. Also, various other acids such as sulfuric. formic, citric, tartaric, acetic, lactic, phosphoric, and hydrofluoric may be used with these inhibitors.

In the preparation of the metal surface for the pickling bath, it is preferable to first free the metal from grease by dipping in an organic solvent or an alkali or by the addition of a wetting agent. In the examples, the concentration of the acid or the temperature of the solution may be varied as desired. The proportions of the inhibitors used "may vary likewise, relatively large proportions may at times be necessary to reduce the corrosion of the metal to a minimum. In general, a quantity of between one tenth of a gram and one gram per grams of actual acid content will be found sufiicient, one half of a gram being usually preferred.

It is to be noted that the products of this invention readily attack oxides and scale with a minimum loss of free metal. In every instance, the primary purpose of a pickling bath is the removal of undesirable deposits and incrustations.

In particular, ferrous metals pickled with the products of this invention are cleaned and magnetic blue oxides, phosphates, etc., removed, and the metals acquire a superior finish, with pitting almost completely eliminated. Moreover, the amount of metal and acid consumed is unusually small.

Since many modifications may be made in the foregoing examples, it is to be understood that still other embodiments differing in scope from the above examples can be readily made without exceeding the bounds of this invention which is to be limited only by the scope of the appended claims.

I claim:

1. An inhibitor composition for pickling ferrous metals comprising a non-oxidizing picklin acid solution and a condensation product of formaldehyde with the reaction product of hydrogen sulfide and a substance chosen from the group consisting of diethylene triamine, triethylene tetramine and triethylamine.

2. The process of cleaning and pickling metals which comprises subjecting the metals to the action of a non-oxidizing acid which contains a condensation product of formaldehyde with the reaction product of hydrogen sulfide and a substance chosen from the group consisting of diethylene triamine, triethylene tetramlne and triethylamine.

3. A pickling bath for iron and steel articles comprising a non-oxidizing acid and a .006 to .025% solution of a condensation product of formaldehyde with the reaction product of hydrogen sulfide and a substance chosen from the group consisting of dlethylene triamine, triethylene tetramine and triethylamine.

4. A pickling inhibitor for ferrous metals comprising a condensation product of formaldehyde with the reaction product of hydrogen sulfide and a substance chosen from the group consisting of diethylene triamine, triethylene tetramine and triethylamine.

WILLIAM H. HILL. 

